21082905 has 12 divisors (see below), whose sum is σ = 36543780. Its totient is φ = 11244192.

The previous prime is 21082903. The next prime is 21082939. The reversal of 21082905 is 50928012.

It can be written as a sum of positive squares in 2 ways, for example, as 6245001 + 14837904 = 2499^2 + 3852^2 .

It is not a de Polignac number, because 21082905 - 2¹ = 21082903 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21082903) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 234210 + ... + 234299.

It is an arithmetic number, because the mean of its divisors is an integer number (3045315).

Almost surely, 2^21082905 is an apocalyptic number.

It is an amenable number.

21082905 is a deficient number, since it is larger than the sum of its proper divisors (15460875).

21082905 is a wasteful number, since it uses less digits than its factorization.

21082905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 468520 (or 468517 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 21082905 is about 4591.6124618700. The cubic root of 21082905 is about 276.2550021958.

The spelling of 21082905 in words is "twenty-one million, eighty-two thousand, nine hundred five".